Unfortunately, there are a number of factors that may make this undesirable:
- At this point in time, Apple does not sell or support their devices in Bangladesh. If your goal is to purchase an iPhone in the U.S., you or someone you know would have to either physically be in the U.S. to do so using a credit line associated with a U.S. banking institution.
- A U.S. phone may not work with the cellular carriers that are available in Bangladesh.
- Apple does not ship to foreign countries from the point of sale, so you, or that someone you know, would have to take care of how the phone gets to Bangladesh.
- Apple does not have an international warranty for iPhones. That means, should your phone need repair, it would have to be shipped back to the country of purchase for those repairs. Apple does not accept them. It would require that you send it to someone you know who can then take it to an Apple Store or Apple Authorized Service Provider for that repair ... and they would have to ship it back to you once done. All shipping charges would be at your expense.
... so you can see, getting an iPhone in this manner may not be optimal for these reasons.